1. Field of the Invention:
This invention relates to machine tools and more specifically to machine tools including means for automatically controlling the operation thereof.
2. Description of the Prior Art:
In an industrial society there is a constant demand for large quantities of identical parts for use in manufacturing a wide variety of articles. Many types of parts are produced by performing a repetitive mechanical operation upon stock material using a machine tool. One type of machine tool employs a rotating spindle to perform operations such as grinding or boring. Another type of machine tool uses a reciprocating hammer or ram to perform functions such as forging, planning, swagging, or punching. Both types perform repetitive operations, with each operation cycle having a substantially equal time period, i.e., the time required for a spindle to make one revolution or the time required for a ram to complete one stroke and return to its starting position.
Automatic operation of these machines allows repetitive cycling without the need for an operator to initiate each cycle. A large number of operations are performed per unit of time in this manner. However, the typical machine does not have the ability to detect improper operations. For example, it is not unusual for a punch press to produce hundreds of unusable parts because of a faulty die, improper stock feeding, or failure of lubrication. These malfunctions are detected and corrected by quality control personnel and machine operators.
Even more serious is the not infrequent occurrence of a foreign body becoming wedged between the tool surfaces. In a punch press, for example, this can result in a badly damaged die or even a damaged press. When this happens it is necessary to halt operation of the press and repair or replace the damaged components before production can resume. Since a damaged die can cost hundreds or even thousands of dollars to repair, the cost of maintenance and repair of dies is a significant fraction of the cost of operating an automatic punch press facility.
It would be desirable to provide a system which can detect improper machine tool operation and take corrective action before producing a large quantity of faulty parts or damaging the tool. One device for detecting improper operation of a punch press is described in U.S. Pat. No. 3,444,390 issued to Victor S. Breidenbach and Patrick V. Close. This device employs a piezoelectric transducer to detect accelerating disturbances produced by the punch press. Peak amplitudes produced by the transducer during normal operation of the punch press are compared to peak amplitudes produced by the transducer during subsequent operation of the punch press. If a signal peak from the transducer is greater than peaks produced during normal operation, the device will shut down the punch press.
Abnormally large peaks are produced when foreign material lodges in the punch press or upon occurrence of some other serious malfunctions. However, many types of irregular or abnormal machine tool operation do not produce abnormally large peaks, including conditions leading to serious failures. Thus, many types of malfunctions are not detected by merely monitoring peak amplitudes of signals produced by the transducer. It is desirable to provide an automatic machine tool system which would detect other types of abnormal operation including die wear or lack of lubrication. It is also desirable to provide a system providing highly automated operation requiring a minimum of operator action and calibration at startup, thereby providing a versatile machine which is easily set up for different jobs.